1. Field
The disclosed embodiments relate to communications. More particularly, the disclosed embodiments relate to a method and apparatus for transmitting and receiving variable rate packets of data with signals indicative of the data rate of those packets.
2. Background
The use of Code Division Multiple Access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and AM modulation schemes such as Amplitude Companded Single Sideband (ACSSB) are known, CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d assigned to the assignee of the present invention, and incorporated by reference herein.
CDMA systems often employ a variable rate encoding of data so that the data rate can be varied from one data frame to another. An exemplary embodiment of variable rate encoding is described in U.S. Pat. No. 5,414,796, entitled xe2x80x9cVARIABLE RATE VOCODER,xe2x80x9d assigned to the assignee of the present invention, and incorporated by reference herein. The use of a variable rate communications channel reduces mutual interference by eliminating unnecessary transmissions when there is no useful data to be transmitted. Algorithms are utilized during encoding for generating a varying number of information bits in each frame in accordance with variations in data activity. For example, an encoder of a cdma2000 1xc3x97EV-DV system may produce 20 millisecond (ms) data frames containing 0, 168, 360, 744, 1512, 3048, 6120, 12264, or 20456 bits of data, for transmission on the reverse link. It is desired to transmit each data frame in a fixed amount of time by varying the transmission rate of communications.
Additional details on the formatting of the data into data frames are described in U.S. Pat. No. 5,511,073, entitled xe2x80x9cMETHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION,xe2x80x9d assigned to the assignee of the present invention, and incorporated herein by reference. The data frames may be further processed, spread spectrum modulated, and transmitted as described in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d assigned to the assignee of the present invention, and incorporated by reference herein.
Variable rate systems can be developed which include explicit rate information. If the rate is included as part of a variable rate frame, then the rate is not recoverable until after the frame has already been properly decoded, at which point the rate has already been determined. Rather than including the rate in the variable rate frame, the rate could instead be sent in a non-variable rate portion of the frame. However, only a few bits are typically needed to represent the rate, and these bits cannot be efficiently encoded and interleaved in order to provide error protection for fading communications channels. Furthermore, the rate information is only available after some decoding delay or subject to error.
Alternatively, variable rate systems can be developed which do not include explicit rate information. One technique for the receiver to determine the rate of a received data frame where the rate information is not explicitly included in the frame is described in U.S. patent application No. 5,566,206, entitled xe2x80x9cMETHOD AND APPARATUS FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA IN A COMMUNICATIONS RECEIVER,xe2x80x9d assigned to the assignee of the present invention, and incorporated by reference herein. Another technique is described in U.S. Pat. No. 5,710,784, entitled xe2x80x9cMULTIRATE SERIAL VITERBI DECODER FOR CODE DIVISION MULTIPLE ACCESS SYSTEM APPLICATIONS,xe2x80x9d assigned to the assignee of the present invention, and incorporated herein by reference. According to these techniques, known as blind decoding, each received data frame is decoded at each of the possible rates. Error metrics, which describe the quality of the decoded symbols for each frame decoded at each rate, are provided to a processor. The error metrics may include Cyclic Redundancy Check (CRC) results, Yamamoto Quality Metrics, and Symbol Error Rates. These error metrics are well-known in communications systems. The processor analyzes the error metrics and determines the most probable rate at which the incoming symbols were transmitted.
Decoding each received data frame at each possible data rate will eventually generate the desired decoded data. However, the search through all possible rates is not the most efficient use of processing resources in a receiver. Also, as higher transmission rates are used, power consumption for determining the transmission rate also increases because there are more bits per frame to be processed. Furthermore, as technology evolves, variable rate systems may utilize larger sets of data rates for communicating information. The use of larger sets of rates will make the exhaustive decoding at all possible rates infeasible. The decoding delay will not be tolerable for some system applications. Consequently, there is a need for a more efficient explicit rate determination system in a high data rate variable rate communications environment.
Embodiments disclosed herein address the above-stated needs by providing an efficiency enhanced rate determination system for a high data rate variable rate communications environment. In one aspect, in a variable rate wireless communication system having at least a first channel and a second channel, a method for explicitly indicating data rate information includes generating a frame of data from data present on the at least first and second channels, determining a set of all possible data rate combinations for the at least first and second channels, determining a subset of authorized data rate combinations and a subset of unauthorized data rate combinations from the set of all possible data rate combinations, selecting a data rate combination to represent the data present on the at least first and second channels from the subset of unauthorized data rate combinations to represent a data rate combination with at least one zero data rate, and transmitting an indicator of the selected data rate combination and the frame of data.
In another aspect, in a variable rate wireless communication system having at least a first channel and a second channel, a method for explicitly indicating data rate information includes generating a frame of data from data present on the at least first and second channels, determining a set of all possible data rate combinations for the at least first and second channels, determining a subset of authorized data rate combinations and a subset of unauthorized data rate combinations from the set of all possible data rate combinations, selecting a data rate combination with a maximum data rate to represent a channel data rate combination with a zero data rate when the maximum rate is authorized on the zero rate channel, and transmitting an indicator of the selected data rate combination and the frame of data.
In another aspect, in a variable rate wireless communication system having at least a first channel and a second channel, a method for decoding received data using explicit data rate indication information includes receiving a frame of data comprising data present on the at least first and second channels and a rate combination indictor indicating a data rate for the at least first and second channels, determining a set of all possible data rates for the at least first and second channels, determining a subset of authorized data rates and a subset of unauthorized data rates from the set of all possible data rates for the at least first and second channels, and processing a channel having an unauthorized data rate as a zero rate channel, without declaring an erasure or adjusting the setpoint.
In yet another aspect, in a variable rate wireless communication system having at least a first channel and a second channel, a method for decoding received data using explicit data rate indication information includes receiving a frame of data comprising data present on the at least first and second channels and a rate combination indictor indicating a data rate for the at least first and second channels, determining a set of all possible data rates for the at least first and second channels, determining a subset of authorized data rates and a subset of unauthorized data rates from the set of all possible data rates for the at least first and second channels, processing a channel having an authorized data rate and no recovered data by measuring the signal to noise ratio and comparing the ratio to a threshold determined by the indicated rate, and processing a channel where the ratio is below the threshold as a zero rate channel, without declaring an erasure or adjusting the setpoint.
In still another aspect, a base station being configured to encode a signal for transmission includes, a transmitter, the transmitter capable of transmitting variable rate data signals between a base station and a remote terminal, and a processor communicatively coupled to the transmitter and configured to: generate a frame of data from data present on the at least first and second channels, determine a set of all possible data rate combinations for the at least first and second channels, determine a subset of authorized data rate combinations and a subset of unauthorized data rate combinations from the set of all possible data rate combinations, select a data rate combination to represent the data present on the at least first and second channels from the subset of unauthorized data rate combinations to represent a data rate combination with at least one zero data rate, select a data rate combination with a maximum data rate to represent a channel data rate combination with a zero data rate when the maximum rate is authorized on the zero rate channel, and transmit an indicator of the selected data rate combination and the frame of data.
In another aspect, a remote terminal configured to receive a transmitted signal includes a receiver, the receiver capable of receiving variable rate data signals from a base station, and a processor communicatively coupled to the transmitter and configured to: receive a frame of data comprising data present on the at least first and second channels and a rate combination indictor indicating a data rate for the at least first and second channels, determine a set of all possible data rates for the at least first and second channels, determine a subset of authorized data rates and a subset of unauthorized data rates from the set of all possible data rates for the at least first and second channels, process a channel having an unauthorized data rate as a zero rate channel, without declaring an erasure or adjusting the setpoint, process a channel having an authorized data rate and no recovered data by measuring the signal to noise ratio and comparing the ratio to a threshold determined by the indicated rate, and process a channel where the ratio is below the threshold as a zero rate channel, without declaring an erasure or adjusting the setpoint.
In another aspect, a variable rate wireless communications system includes a base station for encoding and transmitting data with a reduced-bit rate combination indicator explicitly indicating the rate of the data, and a remote terminal for receiving and decoding data using the reduced-bit rate combination indicator without declaring erasures or adjusting the setpoint when processing a channel with a zero data rate.